CODEWITHSUNDEEP
databasesqlitepython-3.xforeign-keys
Ollie
Ollie

Reputation: 1134

SQLite3 + Python3 - creating a database with foreign keys

Hi there everyone,

I'm having a little trouble with sqlite3 and python3. I think I'm having one of those dumb moments again, but I'm trying to essentially trying to make the table below.

The sticking point seems to be the foreign keys - I'm doing something wrong, but I haven't quite worked out what - and my google searches aren't really getting me anywhere. I can't find any good documentation. I've tried multiple different syntax's for foreign key's online, but none are getting me any nearer to a working table.

Database relational view

c.execute('''
          CREATE TABLE Driver (
          ID INTEGER PRIMARY KEY NOT NULL UNIQUE AUTOINCREMENT,
          FirstName text,
          LastName text,
          RegistrationNo text)
          ''')

c.execute('''
          CREATE TABLE Passenger (
          ID INTEGER PRIMARY KEY NOT NULL UNIQUE AUTOINCREMENT,
          FirstName text,
          LastName text)
          ''')

c.execute('''
          pragma foreign_keys=on;
          begin transaction;

          CREATE TABLE Journey (
          ID INTEGER PRIMARY KEY NOT NULL UNIQUE AUTOINCREMENT,
          Driver_ID INTEGER NOT NULL
          FOREIGN KEY (Driver_ID) REFERENCES Driver,
          Origin text,
          Destination text,
          SeatsAvailable integer,
          Date text,
          Time text,
          DriverNotes text,
          PassengerNotes text)
          ''')

c.execute('''
          pragma foreign_keys=on;
          begin transaction;

          CREATE TABLE Assigned Passengers (
          ID INTEGER PRIMARY KEY NOT NULL UNIQUE AUTOINCREMENT,
          Journey_ID INTEGER NOT NULL
          FOREIGN KEY (Journey_ID) REFERENCES Journey,
          Passenger_ID INTEGER NOT NULL
          FOREIGN KEY (Passenger_ID) REFERENCES Passenger
          ''')

One of the messages I'm getting is -

Traceback (most recent call last):
File "/Users/Computer/Bitbucket/Python Project/sql.py", line 46, in <module>
    ''')
sqlite3.Warning: You can only execute one statement at a time.

Line 46 is at the end of the Journey creation block.

Thanks in advance to anyone that can help :)

Upvotes: 5

Views: 3590

Answers (1)

CL.
CL.

Reputation: 180020

  1. As the message tells you, you can only execute one statement at a time.
  2. You need to execute PRAGMA foreign_keys only once for the connection.
  3. Executing BEGIN TRANSACTIOn makes no sense here.
  4. A PRIMARY KEY constraint already implies NOT NULL.
  5. A PRIMARY KEY constraint already implies UNIQUE.
  6. If a table name contains a space, you must quote it.
  7. When you declare a foreign key as a table constraint, you must write it after all the columns, and must not forget the delimiting comma.
  8. When you declare a foreign key as a column constraint, you must use the correct syntax:
c.execute('''
          CREATE TABLE Journey (
              ID INTEGER PRIMARY KEY AUTOINCREMENT,
              Driver_ID INTEGER NOT NULL REFERENCES Driver(ID),
              Origin text,
              Destination text,
              SeatsAvailable integer,
              Date text,
              Time text,
              DriverNotes text,
              PassengerNotes text)
          ''')
c.execute('''
          CREATE TABLE Assigned_Passengers (
              ID INTEGER PRIMARY KEY AUTOINCREMENT,
              Journey_ID INTEGER NOT NULL REFERENCES Journey(ID),
              Passenger_ID INTEGER NOT NULL REFERENCES Passenger(ID))
          ''')

Upvotes: 6

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